This invention relates to a centrifugal separator of the type which can be used to extract heavier materials from a slurry containing the material mixed with other materials.
My published U.S. Pat. Nos. 4,776,833 and 4,608,040 disclose a device of this type which comprises a centrifugal bowl having a base and a peripheral wall surrounding an axis passing through the base and generally upstanding from the base to an open mouth, a plurality or axially spaced inwardly projecting rings mounted on an inner surface of the peripheral wall and a plurality of openings extending through the peripheral wall from the outer surface to the inner surface thereof, the openings being arranged between each ring and the next adjacent ring and in spaced relation around the peripheral wall, means mounting the bowl for rotation about the axis, means for feeding the materials into the bowl so that during rotation of the bowl they flow over the peripheral wall for discharge from the open mouth and means for applying fluid to the outer surface of the bowl so as to pass through the openings and fluidize the materials between the rings, the openings passing through the peripheral wall in a direction inclined to an axial plane passing therethrough so as to tend to direct the fluid around the peripheral wall.
This device has been found to operate very satisfactorily and in a considerably improved manner relative to prior art devices. However it is a batch discharge device in that the material separated between the rings remains between the rings and after a period of time it is necessary to halt operation of the bowl and to wash out the remaining material for collection and final separation to retrieve the gold or other heavier material.
There has long been a need and a desire for a separator of this general type which operates in a continual mode, that is the mixture is fed in at one point and two exit streams are retrieved, one including the heavier materials and the other including the lighter materials.
This requirement has become particularly important when a separator of this type is employed in other industries such as the coal industry for separation prior to combustion of the heavier sulfites from the coal to reduce emission of sulfur dioxide to atmosphere during combustion and such as the steel industry for separation of steel particles from soot. In these cases, the amount of heavy material can make the process inefficient due to the stops necessary for batch discharge.
The present invention provides an improvement over my above described device which allows the separator to discharge in a continuous mode. The centrifugal separator of the present invention therefore provides an arrangement for continuous or substantially continuous separation of heavier materials. The apparatus includes a bowl having an inner surface which has separating means on the inner surface for separating the heavier material from the lighter materials which pass over the wall of the bowl to an open mouth for discharge. The separating means preferably comprises a plurality of axially spaced rings mounted on the wall and projecting inwardly toward the axis of the bowl and defining between each ring and the next ring an annular recess within the heavier materials are collected. At the base of each recess is provided a plurality of angularly spaced discharge openings each of which extend only over a part of the periphery of the bowl so that the majority of the periphery is free from the openings.
In order that the material can escape through the openings, the materials in the recess are fluidized so that they can rotate around the bowl to the next adjacent discharge opening.
This fluidization is effected by the provision of injection holes which are inclined around the bowl and also by optional second injection openings which are arranged around each discharge opening to inject fluid into the area radially inward of the opening. These fluidization jets cooperate to maintain the material within the recess fluidized to ensure that the material can pass to the discharge opening without forming pockets which discharge an stationary material between the discharge openings.
A valve is provided which controls the exit of material through an orifice defining the opening adjacent the surface of the bowl. The chamber diverges outwardly from the orifice to the valve with the valve having a larger diameter or transverse dimension than those dimensions than the orifice so that a slug of material between the orifice and the valve escape without possibility of hang up.
Embodiments of the invention will now be described in conjunction with the accompanying drawings.